1. Technical Field of the Invention
The present invention relates to a biological technique for removing contaminating trace amounts of dihalocarboxylic acids or salts thereof from aqueous solutions of amino acids or amino acid derivatives by treating such solutions with a minor amount of either a microorganism producing an enzyme specific for the decomposition of dihalocarboxylic acids or salts thereof, or with such enzyme, per se.
2. Description of the Prior Art
Aqueous solutions of amino acids or derivatives thereof are especially useful in the field of cosmeticology as surfactants or sequestering agents; since these solutions are contacted with biological entities or membranes, the presence of any impurity likely to contribute to irritation should be avoided.
Among the products and compounds that contribute to irritation, e.g., skin irritation, the dihalocarboxylic acids and salts thereof are especially representative.
Amino acids are typically prepared by condensing an aqueous solution of an amino compound with a halocarboxylic acid or derivative thereof. As a result of their own preparative technique, halocarboxylic acids or derivatives thereof may contain up to 5% by weight of byproduct dihalocarboxylic (in particular dichloro- or dibromocarboxylic) acid.
For example, .alpha.-amino-substituted acetic acids of the formula: ##STR1## in which R is H, an alkyl or alkoxy radical and X is H, an alkali metal or alkaline earth metal or an ammonium residue, are traditionally prepared by condensing a secondary amine of the formula: ##STR2## with chloroacetic acid or salt thereof, in particular sodium chloroacetate.
It has been determined that the final product aqueous solutions may contain up to 500 ppm of dichloroacetic acid or salt thereof. Such amounts can be decreased to 50 ppm by employing a purified chloroacetic acid, but the added cost militates against the economic viability of the final products for their intended applications.
WO-93/20,223 describes decomposing the haloalkanoic acids present as impurities in surfactants by contacting same with a dehalogenase enzyme.
Thus, the monochloropropionic or monochloroacetic acids or sodium salts thereof, present in a proportion of several g/l in aqueous solutions containing 12% by weight of surfactants (ether carboxylates in particular) buffered to pH 7.2 are hydrolyzed by means of Pseudomonas putida NCIB 12018; the organism is employed in the proportion of 2 g/l, namely, 2,000 ppm relative to the medium.
Nonetheless, the aqueous solutions obtained contain an amount of residual cells which are incompatible, from a standpoint both of performance and of biological tolerance, with applications in cosmeticology.